Method of manufacturing pneumatic tire and vulcanizing metal mold used for the method

ABSTRACT

It is a method of manufacturing a pneumatic tire provided with a bead guard having an excellent appearance without forming spews and bare, wherein when a pneumatic tire ( 1 ) provided with a bead guard ( 5 ) of a trapezoidal shape at section is vulcanization-shaped in a split type mold ( 11 ) comprising a pair of annular side rings ( 13 ) and many divided segments ( 12 ) for the formation of a tread portion integrally united and engaged therewith, an edge ( 13 - 1  SE,  13 - 2 iSE) of a dividing face ( 13 - 1 S,  13 - 2 iS) between mutually adjoining side ring pieces ( 13 - 1, 13 - 2 ) formed by annularly dividing a side ring ( 13 ) inward and outward in a radial direction with respect to a center axis line of the split type mold ( 11 ) and located at a side of a tire shaping face is positioned in a place corresponding to a depressing portion ( 15 ) forming a bead guard ( 5 ).

This is a National Stage entry under 35 U.S.C. §371 of InternationalPatent Application No. PCT/JP01/06703 filed Aug. 3, 2001, the entiredisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a method of manufacturing a pneumatic tire anda vulcanization mold used therefor, and more particularly to a method ofmanufacturing a pneumatic tire comprising a bead portion provided with aprotruding portion of, for example, a trapezoidal shape at its section,which is called as a bead guard, through vulcanization-shaping and avulcanization split type mold for realizing the vulcanization-shaping inthis method. Especially, the invention provides a bead guard showing agood appearance.

BACKGROUND ART

In the vulcanization-shaping of a radial ply tire among pneumatic tires,it is general to use a split type mold as a vulcanization mold capableof advantageously coping with a high precision finishing and a varietyof tread patterns in the tire. All the tire described hereinafterindicates a radial ply tire.

The split type mold comprises a pair of side rings forming a pair ofbead portions and a pair of sidewall portions of a pneumatic tire, andmany split segments for the formation of a tread portion of thepneumatic tire each freely going in and out inward and outward in aradial direction with respect to a center axis line of the side ring andengaging with the respective side ring as mentioned later in detail.

An integrally engaged face between the side ring and the segment isexistent in a position corresponding to an inward of the tire treadportion in a radial direction. And also, the side ring has an integrallyengaged face with a bead ring shaping a part of a bead portion extendingoutward from a bead base in the radial direction, more concretely up toa neighborhood of a central position of a flange height of an approvedrim to be mounted with the tire during vulcanization.

When an uncured tire held in the split type mold is subjected to avulcanization-shaping, a pressurized gas is filled into an inner face ofthe uncured tire to push the uncured tire onto the split type mold. As aresult, air reservoirs are created between the split type mold and theuncured tire though the number of the air reservoirs is far less thanthat in a conventional full mold or so-called two-split mold. As thevulcanization proceeds at such a state, a rough face called as bare isformed in a cured tire to remarkably impair an appearance of the tire.

Even in the split type mold, therefore, through-type ventholes forventing air are disposed in many places easily causing the bare. In thiscase, rubber flowed into an inside of the venthole during thevulcanization renders into many spew rubbers protruded from a surface ofa tire after the vulcanization-shaping. Since it is required to removethese spew rubbers at a separate trimming step, there are causedproblems that the number of working steps increases and direct materialcost and industrial waste cost spoil and the appearance is impaired bytrimmed traces.

For this end, it is variously attempted to largely decrease the numberof the ventholes or remove them, but complete removal is not stillattained.

When a pneumatic tire comprising a bead guard is vulcanization-shaped inthe split type mold, an air reservoir is apt to be formed in adepressing portion of the side ring for the formation of the bead guardprotruding outward from the tire on a circumference of the bead portionand frequently shaping into a torus.

The reserved air is compressed through rubber by a pressure of ahigh-pressure gas acting to an inside of an uncured tire. A part of thecompressed air is scattered and lost around the depressing portion,while the remainder is particularly crowded between a corner part of theprotruded portion like the bead guard at the outer surface of the tireand a bottom corner part of the depressing portion of the side ringcorresponding thereto to create the bare in the corner part of the beadguard.

The thus created bare considerably imparts the appearance of the tirebut also causes a problem that the bead guard remarkably comes off froman expected shape.

In order to prevent the occurrence of such bears, it is required todispose many ventholes in the bottom corner part of the depressingportion of the side ring as previously mentioned. In this case, howeverthere are caused the aforementioned problems and also an operation forremoving spews from a top corner part of the bead guard is particularlysuch a delicate operation that damage must not be given to the topcorner part and brings in difficulty at the removal through mechanicaloperation, which is different from the case of removing spews at theother tire positions. Further, since such a protruding portion is easilynoticeable, it is apt to remarkably impart an appearance of the tire bytraces damaging the top corner parts and spew-removed traces.

Therefore, the invention aims at a pneumatic tire comprising a beadguard in its bead portion and is to provide a method of manufacturing apneumatic tire capable of forming a bead guard having an excellentappearance without creating bare trouble and spew in the bead guard anda vulcanization mold usable for carrying out this method.

DISCLOSURE OF THE INVENTION

According to the invention, there is a method of manufacturing apneumatic tire comprising a tread portion, a pair of sidewall portionsand a pair of bead portions communicating with both sides of the treadportion, and a bead guard disposed in at least one bead portion andprotruding outward from the tire by vulcanization-shaping with a splittype mold comprising a pair of annular side rings forming the pair ofbead portions and the pair of sidewall portions and many split segmentsfor the formation of the tread portion integrally united and engagedwith the respective side ring, characterized in that an edge of adividing face between mutually adjoining side ring pieces by annularlydividing the side ring inward and outward in a radial direction withrespect to a center axis line of the split type mold and located at aside of a tire shaping face is positioned in a place corresponding to adepressing portion forming a bead guard, more preferably a placecorresponding to a bottom of the depressing portion.

It is favorable that the edge of the dividing face between the mutuallyadjoining side ring pieces located at the side of the tire shaping faceis positioned in a place corresponding to a corner part of thedepressing portion forming the bead guard.

When an uncured tire is pushed onto a shaping face of the mold, air iseasily escaped into such a place that a flow-displaced or deformedrubber of the uncured tire arrives at the shaping face of the mold at arate slower than that of the other rubber portion and hence the bare iseasily caused in such a place, so that when there are plural cornerparts, it is favorable to position the edge of the dividing face betweenthe mutually adjoining side ring pieces located at the side of the tireshaping face in a place corresponding to a deeper corner part.

On the other hand, when the uncured tire is gradually enlarged anddeformed from inward to outward in the radial direction by using, forexample, a shaping bladder in the vulcanization-shaping, it is favorablethat the edge of the dividing face between the mutually adjoining sidering pieces located at the side of the tire shaping face is positionedin a place corresponding to an outward corner part in the radialdirection at a side delaying the enlarging deformation of the uncuredtire among corner parts adjoining to each other inward and outward inthe radial direction in the depressing portion forming the bead guard.

A vulcanization mold usable for carrying out the manufacturing methodaccording to the invention is a vulcanization split type mold comprisinga pair of annular side rings forming a pair of bead portions and a pairof sidewall portions of a pneumatic tire, many split segments for theformation of a tread portion of the pneumatic tire each freely going inand out inward and outward in a radial direction with respect to acenter axis line of the side ring and engaging with the respective sidering and a depressing portion formed in at least one side ring for theformation of a bead guard protruding outward from the pneumatic tire inthe bead portion, and is characterized in that the side ring isconstructed with two or more side ring pieces annularly divided inwardand outward in a radial direction with respect to a center axis line ofthe split type mold, and the depressing portion is formed in at leasttwo adjoining side ring pieces, and an edge of a dividing face betweenthe mutually adjoining side ring pieces located at a side of a tireshaping face is positioned in the depressing portion, preferably abottom of the depressing portion.

In a preferable embodiment of such a mold, the edge of the dividing facebetween the mutually adjoining side ring pieces disposed in thedepressing portion and located at the side of the tire shaping face ispositioned in a corner part at the bottom of the depressing portion.

When plural corner parts are existent in the bottom of the depressingportion forming the bead guard, it is favorable that the edge of thedividing face between the mutually adjoining side ring pieces formingthe depressing portion and located at the side of the tire shaping faceis positioned in a deepest bottom corner part among the plural bottomcorner parts, or that the edge of the dividing face between the mutuallyadjoining side ring pieces forming the depressing portion and located atthe side of the tire shaping face is positioned in an outward bottomcorner part in the radial direction among the plural bottom corner partsseparated away from each other in the radial direction of the depressingportion.

Thus, as previously mentioned, ventilation can be smoothly and surelyrealized from such a most easily air reserving portion that the uncuredtire most lately contacts with the tire shaping face of the mold.

Preferably, each of the side rings is divided into three or more sidering pieces.

More preferably, a chamfered portion specifying a position of the edgeof the dividing face located at the side of the tire shaping face isformed in at least one of the mutually adjoining side ring pieces.

Further, it is favorable that the side ring pieces in each of the siderings have a structure capable of assembling and dissembling them andare integrally united with each other in a vulcanization work includingopen-close of a vulcanizing machine provided with the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatically right-half section view of a vulcanizationmold according to the invention together with a pneumatic tirevulcanization-shaped therein.

FIG. 2 is an enlarged section view of a main part of the tire shown inFIG. 1.

FIG. 3 is an enlarged section view of a main part of the split type moldshown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

A pneumatic tire (hereinafter referred to as a tire) 1 showing only asectional outline in FIG. 1 comprises a tread portion 2, a pair ofsidewall portions (only one-side portion is shown) 3 and a pair of beadportions (only one-side portion is shown) 4 communicating with bothsides of the tread portion 2.

At least one of the bead portions 4 is provided with a bead guard 5protruding outward from the tire and extending continuously ordisconnectedly on a circumference of the bead portion so as to takeapproximately an annular shape as a whole. The bead guard 5 may have,for example, substantially a sectional shape of a polygon, a mountain orthe like, and the illustrated embodiment has a sectional shape of atrapezoid. Moreover, when the tire 1 is a run-flat tire, the bead guard5 is disposed on each of both bead portions 4.

Furthermore, the tire 1 comprises a carcass of one or more rubberizedplies of radially arranged cords and a belt located on an outercircumference of the carcass according to the custom though they are notillustrated.

The tire 1 shown in FIG. 1 is a state just after the completion ofvulcanization-shaping in a cavity of a split type mold 11. The splittype mold 11 usually mounted on a vulcanizing machine (not shown) at ahorizontal state comprises many split segments 12 forming the treadportion 2 of the tire 1 and a pair of upper and lower annular side rings13 forming the pair of the sidewall portions 3 and the pair of the beadportions 4. The segments 12 are arc-shaped bodies of a tread ringdivided in a circumferential direction of the tread portion 2. Thesesegments 12 have a structure of freely going in and out inward andoutward in a radial direction with respect to a center axis line (notshown) of the split type mold 11.

More detailedly, the segments 12 are moved outward from a position shownin FIG. 1 up to a waiting place in a radial direction at a non-workingtime and moved inward in the radial direction at a working time so as tolocate in the position shown in FIG. 1 by a radially moving means (notshown) with respect to the above center axis line.

On the other hand, a lower side ring 13 in the pair of upper and lowerside rings 13 is fixed to a lower portion of the vulcanizing machine,while an upper side ring 13 is fixed to an upper portion of thevulcanizing machine capable of moving in up-down directions. In theinvention, at least one of the side rings 13 is provided with anapproximately annular depressing portion 15 forming the bead guard 5disposed on the bead portion 4 of the tire 1. When each of the beadportions 4 is provided with the bead guard 5, each of the upper andlower side rings 13 is provided with the depressing portion 13.Moreover, a center axis line of the pair of the side rings 13 forms acenter axis line of the split type mold 11 at the above fixationposition. Hereinafter, they are called as a center axis line.

Numeral 16 is a bead ring engaging with the side ring 13 and forming apart of the bead portion 4.

When an uncured tire having a toroidal shape near to the tire 1 isplaced and vulcanization-shaped in the split type mold 11 under theabove structure constituted with the segments 12 and the pair of theside rings 13, the segments 12 are moved inward from the waiting placesin the radial direction and integrally united and engaged with each ofthe pair of the side rings 13.

Here, the side ring 13 provided with the depressing portion 15 isdivided into two or more annular bodies at inside and outside in theradial direction with respect to the center axis line. Each of thesedivided bodies is called as a side ring piece.

The split type mold 11 shown in FIG. 1 comprises three divided side ringpieces 13-1, 13-2, 13-3. They are united together and placed in thevulcanizing machine. In these united side ring pieces 13-1 to 13-3,mutually adjoining dividing faces 13-1S, 13-2 iS as well as 13-2 oS,13-3 iS have an extremely slight space forming an air path but notpermitting flow-in of rubber during the vulcanization-shaping of thetire 1.

As shown in FIGS. 1 and 3, at least two side ring pieces, mutuallyadjoining two side ring pieces 13-1, 13-2 in the illustrated embodimenthave edges 13-1SE, 13-2 iSE of the dividing faces 13-1S, 13-2 iS locatedat a side of a tire shaping face on a bottom 15BS of the depressingportion 15. In the depressing portion 15 is never disposed venthole orthe like.

Thus, when the tire 1 is vulcanization-shaped by using the above splittype mold 11, the edges 13-1SE, 13-2 iSE of the dividing faces 13-1S,13-2 iS of the mutually adjoining side ring pieces 13-1, 13-2 located atthe side of the tire shaping face are position on an outer surface 5OSof the bead guard 5 protruding from the bead portion 4, so that the beadguard 5 is vulcanization-shaped in the depressing portion 15 definedbetween the respective side ring pieces 13-1, 13-2 at inside and outsidein the radial direction with respect to these edges 13-1SE, 13-2 iSE.

During the time ranging from the start of the vulcanization-shaping tothe curing of rubber with the split type mold 11, air trapped andpressurized between rubber forming the bead guard 5 and the depressingportion 15 is smoothly discharged from the edges 13-1SE, 13-2 iSE of theadjoining side ring pieces 13-1, 13-2 through the dividing faces 13-1S,13-2 iS to an outside of the split type mold 11 without forming ventholeor the like in the depressing portion 15, so that the occurrence of bareis effectively prevented.

As a result, not only spew but also “rubber burr” are not formed on thebead guard 5, so that a good, unhurt appearance of the bead guard havingan expected shape can be provided and an extra finishing step isuseless.

Furthermore, the edges 13-1SE, 13-2 iSE located at the side of the tireshaping face are arranged on the adjoining side ring pieces 13-1, 13-2having the depressing portion 15 in at least one of radially innercorner part 15BSEi and radially outer corner part 15BSEo of the bottom15BS of the depressing portion 15 corresponding to radially inner cornerpart 5OSEi and radially outer corner part 5OSEo of the outer surface 5OSof the bead guard 5 protruding from the tire 1, the radially outercorner part 15BSEo in FIGS. 1 and 3.

According to such a structure, in the vulcanization-shaping of the tire1, the edges 13-1SE, 13-2 iSE of the side rings are positioned in atleast one of the radially inner corner part 5OSEi and outer corner part5OSEo at the outer surface 5OS of the bead guard 5, whereby an escapepath can be given to air usually reserved in the corner part of thedepressing portion 15 corresponding to at least one of the corner part15BSEi, 15BSEo of the bottom 15BS.

In this connection, it is favorable to arrange the edges 13-1SE, 13-2iSE located at the side of the tire shaping face on the adjoining sidering pieces 13-1, 13-2 having the depressing portion 15 in the outercorner part 15BSEo of the bottom 15BS of the depressing portion 15forming the radially outer corner part 5OSEo among the corner parts5OSEi, 5OSEo of the outer surface 5OS of the bead guard 5 separated awayfrom each other in the radial direction, or a deeper part among cornerparts 15BSEi, 15BSEo existing in the bottom 15BS of the depressingportion 15, bottom corner part 15BSEo in the illustrated embodiment.

That is, the edges 13-1SE, 13-2 iSE of the dividing faces of the sidering pieces are position in the radially outer corner part 5OSEo amongthe corner parts 5OSEi, 5OSEo of the outer surface 5OS of the bead guard5 separated away from each other in the radial direction, or the deepestbottom corner part 15BSEo of the depressing portion 15 in thevulcanization-shaping of the tire 1, whereby smooth ventilation can beconducted from a most air reservable portion as previously mentioned.

And also, it is favorable that each of the pair of the side rings 13 isconstituted with three or more divided side ring pieces 13-1, 13-2,13-3, . . . 13-n (natural number of not less than n=1). In this way, itis possible to wipe out inferior bare without arranging ventholes ineach side ring 13 contributing to the formation of the sidewall portion3 of the tire 1, namely forming spews in the sidewall portion 3.

Preferably, as shown by a phantom line in FIG. 3, a chamfered portionspecifying edges 13-1SE, 13-2 iSE 13-2 oSE, 13-3 iSE of the dividingfaces located at the side of the tire shaping face is arranged in atleast one of the adjoining side ring pieces 13-1, 13-2 and the adjoiningside ring pieces 13-2, 13-3. FIG. 3 shows a case of arranging thechamfered portions in the radially inner side ring pieces 13-1, 13-2.

The chamfered portion facilitates the flowing of air trapped in thedepressing portion 15 into each of spaces between the dividing faces13-1S and 13-2 iS and between the dividing faces 13-2 oS and 13-3 iS andreduces a pressure of the trapped air flowing into these dividing faces,and hence a thickness of “burr” protruded rubber film is made thinner todevelop an effect of facilitating a burr-removing operation. Besides, afine band-shaped rubber formed in the chamfered portion as shown by aphantom line in FIG. 2 brings about an additional value as an ornamentfor the bead guard 5.

Further, each of the side ring pieces 13-1, 13-2, 13-3 has a structurecapable of assembling and dissembling at the side of the same side ring13, and is favorable to have a structure that the side ring pieces 13-1,13-2, 13-3 are integrally united with each other to form a one-piecetype side ring 13 at a vulcanization shaping time inclusive of openingand closing of a vulcanizing machine provided with a mold or a splittype mold 11.

EXAMPLES

There is provided a radial ply tire for a passenger car having a tiresize of 225/60R15, wherein a carcass is a rubberized ply of polyestercords of 1500 D/2 and is wound around a bead core embedded in each of apair of bead portions 4 from an inside of the tire toward an outsidethereof up to a neighborhood of a maximum tire width to form a turnupportion and a tread portion 2 has a belt therein and each of the pair ofbead portions 4 is provided with a bead guard 5 of a trapezoidal sectionshape and a bead filler rubber.

Five tires of Example 1 are manufactured by vulcanization-shaping with asplit type mold shown in FIGS. 1 and 3 having no chamfered portion,while five tires of Example 2 are manufactured by vulcanization-shapingwith a split type mold having chamfered portions. On the contrary, fivetires of Conventional Example are manufactured by subjecting the sameuncured tire as in the example tire to vulcanization-shaping with aconventional split type mold having many ventholes in positions formingsidewall portion 3 and bead guard 5 and a pair of single side rings. Asan evaluation, presence or absence of bare formation, presence orabsence of spews, appearance of “burrs” and finish state of sidewallportion 3 and bead portion 4 as a whole are observed, respectively. Theobserved results are shown in Table 1.

TABLE 1 Example 1 Example 2 Conventional Example Presence or absenceabsence presence absence of burr formation Presence or absence absencepresence of many spews absence of formation of substantially requirespew removing spews burr some burrs no burr work spew removal isappearance difficult at corner part of bead guard Finish state ofsubstantially no problem irregular removal of spew, bead portion - noproblem, very good presence of cut damage at sidewall good corner partof bead guard, portion poor appearance

As seen from the results of Table 1, the appearance in the bead guard 5and the sidewall portion 3 is considerably improved in the tires ofExamples 1 and 2 as compared with the conventional tire, and the work ofremoving spews in these portions is omitted and hence the productivityis improved. In the comparison between the tires of Examples 1 and 2,the chamfering is effective in view of the formation of “burr”.

INDUSTRIAL APPLICABILITY

According to the invention, the side ring in the split type mold is auniting system of annular divided side ring pieces and an edge of adividing faces between mutually adjoining side ring pieces located at aside of a tire shaping face is positioned in a place corresponding to abottom of depressing portion for the formation of a bead guard toprevent the formation of bare without forming spews on a bead guard of apneumatic tire, whereby there can be manufactured a pneumatic tireprovided with a bead guard having a given accurate shape and anexcellent appearance.

What is claimed is:
 1. A method of manufacturing a pneumatic tirecomprising a tread portion, a pair of sidewall portions and a pair ofbead portions communicating with both sides of the tread portion, and abead guard disposed in at least one bead portion and protruding outwardfrom the tire by vulcanization-shaping with a split type mold comprisinga pair of annular side rings forming the pair of bead portions and thepair of sidewall portions and many split segments for the formation ofthe tread portion integrally united and engaged with the respective sidering, characterized in that an edge of a dividing face between mutuallyadjoining side ring pieces by annularly dividing the side ring inwardand outward in a radial direction with respect to a center axis line ofthe split type mold and located at a side of a tire shaping face ispositioned in a place corresponding to a depressing portion forming abead guard.
 2. The method according to claim 1, wherein the edge of thedividing face between the adjoining side ring pieces located at the sideof the tire shaping face is positioned in a place corresponding to abottom of the depressing portion.
 3. The method according to claim 1,wherein the edge of the dividing face between the adjoining side ringpieces located at the side of the tire shaping face is positioned in aplace corresponding to a corner part of the depressing portion formingthe bead guard.
 4. The method according to claim 1, wherein the edge ofthe dividing face between the adjoining side ring pieces located at theside of the tire shaping face is positioned in a place corresponding toa deeper corner part among plural corner parts of the depressing portionforming the bead guard.
 5. The method according to claim 1, wherein theedge of the dividing face between the adjoining side ring pieces locatedat the side of the tire shaping face is positioned in a placecorresponding to an outward corner part in the radial direction at aside delaying the enlarging deformation of the uncured tire among cornerparts adjoining to each other inward and outward in the radial directionin the depressing portion forming the bead guard.
 6. A vulcanizationsplit type mold comprising a pair of annular side rings forming a pairof bead portions and a pair of sidewall portions of a pneumatic tire,many split segments for the formation of a tread portion of thepneumatic tire each freely going in and out inward and outward in aradial direction with respect to a center axis line of the side ring andengaging with the respective side ring and a depressing portion formedin at least one side ring for the formation of a bead guard protrudingoutward from the pneumatic tire in the bead portion, characterized inthat the side ring is constructed with two or more side ring piecesannularly divided inward and outward in a radial direction with respectto a center axis line of the split type mold, and the depressing portionis formed in at least two adjoining side ring pieces, and an edge of adivided face between the mutually adjoining side ring pieces located ata side of a tire shaping face is positioned in the depressing portion.7. A vulcanization split type mold according to claim 6, wherein theedge of the dividing face between the adjoining side ring piecesdisposed in the depressing portion and located at the side of the tireshaping face is positioned in a bottom of the depressing portion.
 8. Avulcanization split type mold according to claim 6, wherein the edge ofthe dividing face between the adjoining side ring pieces disposed in thedepressing portion and located at the side of the tire shaping face ispositioned in a corner part at the bottom of the depressing portion. 9.A vulcanization split type mold according to claim 6, wherein the edgeof the dividing face between the adjoining side ring pieces forming thedepressing portion and located at the side of the tire shaping face ispositioned in a deepest bottom corner part among plural bottom cornerparts of the depressing portion.
 10. A vulcanization split type moldaccording to claim 6, wherein the edge of the dividing face between theadjoining side ring pieces forming the depressing portion and located atthe side of the tire shaping face is positioned in an outward bottomcorner part in the radial direction among plural bottom corner partsseparated away from each other in the radial direction of the depressingportion.
 11. A vulcanization split type mold according to claim 6,wherein each of the side rings is divided into three or more side ringpieces.
 12. A vulcanization split type mold according to claim 6,wherein a chamfered portion specifying a position of the edge of thedividing face located at the side of the tire shaping face is formed inat least one of the mutually adjoining side ring pieces.
 13. Avulcanization split type mold according to claim 6, wherein the sidering pieces in each of the side rings have a structure capable ofassembling and dissembling them and are integrally united with eachother in a vulcanization work inclusive of opening and closing of avulcanizing machine provided with the mold.